The respiratory protein in marine worms is termed hemerythrin. In the coelomic fluid of Themiste zostericola it is an octamer and in the retractor muscle it is a monomer. A comparison of the chemical properties of the octamer and monomer has been, and will be, made. The kinetics of important physiological and preparative reactions will be determined including oxygenation and autoxidation, reduction of the fully oxidized met form and oxidation of the fully reduced, deoxy form. The role of the semi-met form will be delineated. Conventional, rapid flow, pulse radiolysis and EPR methods have been, and will continue to be, used. A comparison will be made of these reactions with hemerythrin from other worm species, e.g., Phascolopsis gouldii; mammalian respiratory proteins myoglobin and hemoglobin; and other polynuclear (iron-sulfur) proteins.